Electrically heated screen construction



United States Patent ELECTRICALLY HEATED SCREEN CONSTRUCTION Thomas W. Hannon, Canton, Ohio Application July 10, 1952, Serial No. 298,103 12 Claims. (Cl. 209-238) The invention relates generally to electrically heated screens made of conducting material, and more particularly to electrically heated screens used for the industrial screening of materials. When motion is imparted to such screens, there are two principal types known as vibrating screens, and hummer screens. In a vibrating screen, the frame mounting the screen is oscillated. In a hummer screen, the frame mounting the screen is stationary, and motion is imparted to the screen itself as a diaphragm by a rapidly reciprocating armature connected to the screen and operated by an alternating current solenoid coil.

When screens used for industrial screening of materials are electrically heated, much less blinding or clogging of the screens takes place than when operated without electrical heating. The electrical heating of such screens is desirable in many existing industrial material screen installations which have previously been operated without electrical heating, and which it is desired to equip with electrically heated screens, with a minimum change in other parts of the installation.

In my prior application for United States Letters Patent, Serial No. 266,378, filed January 14, 1952, there is set forth electrically heated screen construction embodied in a vibrating screen. Prior to the construction set forth in said application, conventional electrically heated screens have included copper conductor or bus bars bolted to the top of the screen cloth along the sides thereof, with backup bars on the bottom side of the cloth, cables being attached to the conductor bars for supplying current thereto. For efiicient heating, the copper cables must be connected to the conductor bars at relatively short intervals, so that for a long screen the cables would be connected to both ends of the conductor bars as well as to the central portions.

The principal objection to this conventional construction is the large amount of labor involved in replacing the screen cloth when worn, and disconnecting and reattaching the conductor bars to the new cloth. This operation involves removing and reconnecting a large number of bolts for attaching the conductor bars to the screen cloth, and also disconnecting and reattaching the several copper cables carrying current to the copper conductor bars.

Another objection to this conventional construction is that all of the conductor cables as well as the conductor bars are above the screen where they are subjected to the constant abrasion of the material passing over and through the screen. Moreover, where a multi-deck screen is used having two or more decks of screen cloth, the bottom deck is the one most desirably heated, but it is not practical to support the required large quantity of cables between the bottom deck and an upper deck because of the limited amount of space available.

In certain prior constructions, it has been attempted to overcome some of the foregoing difiiculties by making the skirt boards which clamp the sides of the screen cloth of copper to act as conductor or bus bars, and

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connecting the conductor cables to one end of the bars. Such a construction is very expensive. Because of the special shape of the skirt board having a relatively thick cross section, and being made entirely of copper, the overall weight of the copper skirt board is relatively great. A 5 foot section may weigh as much as 400 pounds. Moreover, a uniform temperature cannot be maintained throughout the screen cloth because of the voltage drop from the end connected with the conductor cables to the other end. This extremely heavy weight makes the copper skirt board ditficult to handle when screen replacements are required. Moreover this type of all copper skirt board is subject to abrasion by material passing over the top of the screen, and where extremely abrasive material is being screened, such as coke breeze or slag, these all copper skirt boards wear out in a short time. It is also necessary, where the bottom deck of a double deck screen unit is to be electrically heated, that the copper cable connections be bolted to the all copper skirt board at one end or the other of the screen assembly. In such an assembly, 6 feet wide and 16 feet long, it is necessary that the skirt boards be made in lengths of 4 feet, and a copper jumper bolted between the joining lengths, so that the current will pass from one end of the screen to the other. Because of this arrangement, each time screen cloths are changed, it is necessary for the screen maintenance man to crawl between the two decks of the screen assembly and unbolt these skirt board bus bar connections so that the skirt boards may be lifted up out of the way.

In certain other prior constructions, it has been attempted to overcome some of the foregoing difficulties by a construction including a copper angle running the entire length of the inside of each side plate of the screen assembly. A steel skirt board is tcnsioned against this copper angle at the top and the hook strip of the screen cloth at the bottom. There are two main difficulties with this type of installation. First, the current must pass through the steel skirt board before entering the screen cloth, which results in a power loss because the skirt board offers resistance to the flow of the current and heating takes place within the steel skirt board. Second, a poor contact point exists at the top of the skirt board where it rests against the copper angle bar.

The objects of the present invention include generally the provision of a new and improved composite skirt board construction for an electrically heated screen unit which is adapted for use in many different types of installations, and which is particularly adapted for use in installations where motion is imparted to the screen, and which overcomes objectionable features of prior constructions.

More particularly, the objects of the present invention include the provision of such a new and improved composite skirt board construction for an electrically heated screen unit which is specifically adapted for use either as original equipment in vibrating or hummer screens, or as quick change attachments for existing vibrating or humrner screens.

More specifically, a further object of the present invention is to provide such a new and improved composite skirt board construction for an electrically heated screen unit, by means of which the screen deck may be quickly and easily replaced, without disconnecting the lead conductors from the current conducting bus bars which contact the screen deck.

Another object of the present invention is to provide such a new and improved composite skirt board construction for an electrically heated screen unit in which the conductor bus bars are substantially protected from abrasion by the material being screened, and with minimum insulation required for the conductor bus bars.

A further objectof the present invention is to provide such a new and improved composite skirt board construction for an electrically heated screen unit having a simplified construction and arrangement of parts, permitting economical manufacture and maintenance, and convenience in use.

The foregoing and other objects. are attained by the composite skirt board construction for an electrically heated screen unit, parts, combinations, and sub-combinations, which comprise the present invention or discovcry, and the nature of which is set forth in the following general statement, and preferred embodiments of which are set forth in the following description, and which are particularly and distinctly pointed out and set forth in. the appended claims forming. part hereof.

The nature of the present invention may be stated in general terms as embodying composite skirt board construction for an electrically heated screen unit and the like, including a web with an upper border portion and a lower border portion and a face which in use is an, out side: face. The web is adapted for insulated mounting on a frame side member. A tongue bar is secured to and extends along the outside face of the lower border portion of the web. The tongue bar is made of high conductive material, such as copper, and the web is made of lower conductive material such as steel. The tongue bus bar has a V cross-section, and preferably has a solid V wedge cross-section. The means connecting the tongue bus bar with the web preferably include a plurality of lugs protruding beyond an upper face of the bus bar. Each lug is formed With a hole registering with a hole in the web. A shanked connector extends through each set of registering apertures.

By way of example embodiments of the new and improved composite skirt board construction for electrically heated screen units and the like, and components parts of the present invention are illustrated in the accompanying drawing forming part hereof, in which:

Figure l is a fragmentary transverse sectional view of one embodiment of the new and improved composite skirt board construction with an insulated hinge connection with a frame side member of an electrically heated hummer screen unit;

Fig. 2 is a fragmentary elevational view thereof, looking in the direction of the arrows 22, Fig. 1;

Fig. 3 is a view similar to Fig. l of another embodiment of the new and improved composite skirt board construction which has an insulated bolt and nut mounting on a frame side member of an electrically heated hummer screen unit;

Fig. 4 is a fragmentary front elevation of a preferred improved bus bar for the improved composite skirt board construction; and

Fig. 5 is an end elevation of the bus bar of Fig, 4.

Similar numerals refer to similar parts throughout the several views of the drawing.

In Fig. 1 there is shown a portion of an electrically heated hummer screen unit indicated generally by 10, and which is completely set forth in my application for United States Letters Patent, Serial No. 291,683, filed June 4, 1952.

The electrically heated hummer screen unit includes an open ended frame indicated generally by 11 and having a longitudinally extending side channel 12a which is one of the main supporting members of the unit.

The channel 12a includes top and bottom horizontal flanges 13a and 14a, and a vertical web 15a. The top and bottom flanges of the channel extend outwardly and the web of the channel has a smooth inside face.

The frame 11, as shown, also includes a central bridge member 16 having a downwardly extending end. flange 17a secured by bolt and nut sets 18 to the channel web 15a. The bridge end flange 17a has an outside face abutting the inside face of the channel web 15a.

One of the improved composite skirt boards 19a of the present invention extends longitudinally along the inside face of channel web 15a and a pair of improved insulated hinges one of which is indicated generally by 20 pivotally connect the upper longitudinally extending border portion of the web 21a of the skirt board 19a to the upper portion of the channel web 15a adjacent the top flange 13a. The upper border portion of the web 21a terminates in a longitudinally extending free edge.

The composite skirt board 19a also includes a longitudinally extending improved bus bar 22a secured to the lower edge border portion of the web 21a on the outside face thereof opposite the inside face of the channel web 15a. The bus bar 22a has a transversely bevelled crosssection, and constitutes a V-tongue bus bar having a solid V wedge cross section. The bus bar 22a is made of high conductive material, such as copper.

A screen deck 23 of screening made of lower conductive material such as steel or stainless steel wire, extends laterally between the channel 12a and an opposite similar channel not shown, and longitudinally the entire length thereof, and below the composite skirt board 19a and an opposite similar skirt board not shown. On the longi tudin'al edge border portion of the screen deck 23 ad jac'ent the channel 12a, there is secured a longitudinally extending hook bar 24a having a V cross-section, and constituting a two ply V-groove angle hook bar. One leg of the angle hook bar 240 is horizontal, and the other leg thereof extends upwardly and laterally away from the channel 12a, and presents its V-groove for engagement by the V-tongue of the bus bar 22a, the hook bar being of conducting material such as steel or copper, and the screen deck border portion being formed with a V'- groove fitting between the plies of the V-groove of' the hook bar.

Similarly, an oppositely opening V-groove angle hook bar not shown is secured to the longitudinal edge V- groove border portion of the screen deck 23 adjacent the other channel not shown. The other hook bar and screen deck V-groove border portion present their V-groove for engagement by the V-tongue of the bus bar of the other composite skirt board.

When the grooves of the screen deck border portions and the hook bars are engaged by the tongues of the bus bars, the composite skirt boards have tension applied thereto for swinging them about their respective hori- 'zontal pivotal connections with the mounting channel webs. This stretches the screen deck 23 laterally between the side channels.

Means for applying this tension on the skirt boards and the screen deck 23 are provided as shown by a plurality of insulated clamp bolt and nut sets 25 for each skirt board. Each insulated clamp bolt and nut set 25 operates between its skirt board and the adjacent channel.

One of the insulated clamp bolt and nut sets 25 is shown in detail in Fig. 1, together with the construction details of associated parts. Referring to this particular insulated clamp bolt and nut set 25, the skirt board web 21a has a circular hole 26 formed therein above'the bus bar 22a. The channel web 15a has a larger hole 27 formed therein, at a lower level than the hole 26. An angled thrust plate 28 is secured on the outside of the channel web 15a, and has formed therein a hole 29 opposite the channel web hole 27.

A cylindrical sleeve 30 of insulating material fits in the skirt board web hole 26, and extends from the 0p: posite sides thereof. A washer 31 of insulating material fits on the sleeve 30 on the inside of the skirt board web 21a, the outside face of the washer 31 abutting the inside face of the skirt board web, and the inside end face of the sleeve 30 and the inside face of the washer 31 being flush.

A carriage bolt 32 has a. shank 33 extending through the holes 29 and 27, and the bore of the sleeve 30. The

head 34 of the carriage bolt is on the outside of and abuts against the thrust plate 23. The threaded inner end 35 of the bolt shank 33 extends beyond the washer 31 on the inside of the skirt board web 210. A metal washer 36 is located on the shank end 35 against the insulating washer 31, and a nut 37 is screwed on the threaded shank end 35 against the washer 36.

The insulating washer 3i and the insulating sleeve 30 together constitute a shouldered tubular insulator, interposed between the metallic bolt shank 33, and Washer 36 and nut 37. Thus the clamping bolt and nut set 25 and the frame 11 are insulated from the skirt board 19a.

One of the improved insulated hinges is illustrated in detail in Figs. 1 and 2, and includes a U-bracket 40 having a web 41 secured to the channel web 150! by a bolt and nut set 42. Laterally spaced legs 43 of the U-bracket 40 extend inwardly from the web 41, and the legs 43 have aligned holes formed therein. A swinging hinge member 45 has lower strap members 46 folded on each other and forming an upper sleeve member 47. The lower strap members are connected to the upper portion of the skirt board web 21a.

An insulating sleeve 48 extends through the strap sleeve member 4-7 and beyond the ends thereof. An insulating washer 49 is located on each end of the insulating sleeve 48 beyond the strap sleeve member 47 which is made of steel or other metal. The insulating sleeve 48 and insulating washers 49 thus form a separable insulating spool which mounts the hinge sleeve member 47. This spool is located between the U-bracket legs 43, the bore of the insulating sleeve 43 registering with the U-bracket leg holes 44. A cotter pin fastened headed hinge pin 50 has its shank extending through the holes 44 and the bore of the sleeve 48, and thus pivotally mounts the insulating spool on the metal bracket 49, and insulates the metal hinge member 45 and other parts of the skirt board 19a from the frame 11.

A solenoid operated vertically reciprocating armature unit not shown is mounted on the bridge member 16 centrally of its span. The armature unit is of usual con-v struction and operation in hummer screen units, and includes a vertically reciprocating armature having an insulated connection with the center of the screen deck 23.

At one end of the bus bar 22a, conductor leads 55a connect the bus bar 22a with one terminal of an electric heater unit, not shown. At the other end of the other bus bar, conductor leads not shown connect the other bus bar with the other terminal of the heater unit. The heater unit may be of usual or special transformer construction adapted to deliver low voltage and high amperage alternating current to the bus bars, thereby heating the high resistance screen deck 23 connected therebetween.

When it is desired to change a worn out screen deck 23, it is only necessary to loosen the clamp bolt and nut sets 25 sufficiently to swing the V-tongue bus bars out of engagement with the \.'-groove hook bars of the screen deck 23. The armature is disconnected from the screen deck 23, and the worn out screen deck may be removed, and a new one installed by reverse operations.

The conductor leads are not required to be disconnected during changing of the screens.

It is apparent that the composite skirt board 19a and other parts of the improved electrically heated screen construction may be easily and quickly assembled with the frame 11 and the armature, either as original equipment or as a quick change attachment.

One of the improved bus bars 22a is shown detached from the composite skirt board 19a in Figs. 4 and 5. The bus bar 22a as above stated has a solid V wedge cross-section, and a plurality of flat faces 22a-1, 2211-2, 2211-3, and 2242-4 angular with respect to each other. The faces 2241-1 and 22a-3 are bottom and top faces parallel with each other as shown. The inside face 22a-4 is perpendicular to the faces 22a-1 and 22a-3 and abuts the outside face of the skirt board web 21a in the composite skirt board 19a. The outer face 2211-2 slopes from an apex with the wider bottom face 22a-1 towards the narrower upper face 22a-3. Each bus bar 22a has a plurality of lugs 220-5 extending upwardly from the upper face 22a-3. Each lug 22a-5 is formed with a hole which registers with a hole in the skirt board web 21a. A nut and bolt set 56 has the shank of the bolt extending through each set of registering holes of each lug 22a-5 and skirt board web 21a, and serves as separable means for connecting the bus bar 22a to the skirt board web 21a. In Fig. 3, there is shown a modified composite skirt board 219a which includes a web 221a of formed sheet steel having an internal spring. A bus bar 222a is connected to the lower border portion of the formed web 221a, which has a channel cross-section with an upper angled flange 221a-1 and a lower-angled flange 222a-2.

A flat frame side member 2120 has an angle 21211-1 secured to its inner face which has a lining strip of insulation material 212a-2 above the angle 21211-1 which also has a lining strip of insulation material 212a-3 on its top face. The web 221a is supported on the frame side member 212a by a plurality of insulated bolt and nut sets 225 which clamp the outer free edge of the web top flange 221a-1 against the insulating strip 21251-2. The

composite skirt board 219a thus has an insulated mounting on the frame side member 212a. The above described parts shown in Fig. 3 are incorporated in an electrically heated hummer screen unit 210 which operates generally like the unit 13.

From a broad standpoint, the disclosures of Figs. 1 and 2, and also of Fig. 3, each constitutes, in combination, a tongue bus bar and laterally adjustable insulated supporting means for the tongue bus bar, the tongue bus bar having a V cross-section with an apex, the apex of the V being the outside edge of the bus bar, the tongue bus bar extending longitudinally and being adapted to engage and contact longitudinally a V-groove at one side of a screen deck, and the bus bar being adapted to tension the screen deck in opposition to means engaging the other side of the screen deck, and the bus bar being adapted for connection with an electric power conductor, and the other side of the screen deck being adapted for connection with an electric power conductor.

Furthermore, from a broad stand-point each of the bus bars 22a and 222a may be described as including a longitudinally extending portion having a polygonal crosssection, and the longitudinally extending bus bar portion having two longitudinally extending V faces making an acute angle with each other and a junction with each other at an apex.

It should be still further pointed out, as clearly shown in Fig. 3, that the web 221a extends from the frame side member 212a and over the bus bar 222a, with the bus bar being connected to the lower portion of this web. Thus, the web 221a forms a cover over the bus bar 222a, thereby protecting this bus bar which may be formed of relatively soft, high electrical conductive material.

Finally, as also clearly shown in Fig. 3, the portion of angle 21211-1 extending away from frame side member 212a beneath the lower face of bus bar 222a, which portion is lined at its side which faces bus bar 222a by a lining strip of insulation material 212a-3, serves to substantially complete the enclosure of bus bar 222a, thereby fully protecting the bus bar 222a from being abraded by material passing through the screen. The strip of insulation material 212a-3 prevents the screen from grounding in the event this screen should be moved downwardly through the adjustment of web 221a. Consequently bus bar 222a has sufficient space between the strip of insulation material 212a-3 and the lower face of bus bar 222a so that the screen may be mounted in engagement against the lower face of bus bar 222a and around the tongue end portion thereof which is nearest to or facing frame side member 212a.

Thus, in the constructions of Figs. 1 and 3 the web or laterally adjustable insulated supporting means for the bus bar extends over and preferably to the screen side of the bus bar, that is, the side thereof opposite from the frame side member, so that the bus bar is protected from the abrading action of material being passed through the screen. Further, as shown in Fig. 3, means may be provided extending outwardly from the frame side member, spaced from and extending beneath the lower face of the bus bar, to provide additional protection to the bus and substantially enclose the same, except for the space necessary to receive and engage the screen against the lower face and tongue end of the bus bar.

When, however, the portion of the frame side member is provided extending beneath and spaced from the lower face of the bus bar, it is preferred to provide the strip of insulation material on this portion on the side thereof facing the lower face of the bus bar. Thus, the screen may abut the lower face of the bus bar and engage around the tongue end thereof, and even though the bus bar and web or adjustable supporting means therefor is moved toward the frame side member, there is no danger of the screen grounding in the event this screen should touch the insulation material on the frame side member extending portion.

In the foregoing description, certain terms have been used for brevity, clearness and understanding, but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such words are used for descriptive purposes herein and are intended to be broadly construed.

Moreover, the embodiments of the improved construction illustrated and described herein are by way of example, and the scope of the present invention is not limited to the exact details of construction.

Having now described the invention, the construction, the operation and use of preferred embodiments thereof, and the advantageous new and useful results obtained thereby; the new and useful constructions, and reasonable mechanical equivalents thereof obvious to those skilled in the art, are set forth in the appended claims.

I claim:

1. In combination, a conducting screen deck having a first side and a second side, means supporting the first side of the screen deck, a first power conductor and a connection between the first power conductor and the first side of the screendeck; the second side of the screen deck having a longitudinally extending groove opening toward the first side of the screen deck; a longitudinally extending support member adjacent the second side of the screen deck; a longitudinally extending tongue bus bar in the groove at the second side of the screen deck; adjusting and connecting means operative between the tongue bus bar and the support member, the adjusting and connecting means being operative to move the tongue bus bar laterally toward and away from the support member; and means insulating the tongue bus bar from the support member.

2. Bus bar and support construction including a longitudinally extending tongue bus bar having a lower face and a tongue end portion, a longitudinally extending frame support member; adjusting and connecting means operative between the tongue bus bar and the support member including a web member having an inner face opposite the support member and an outer face, the bus bar being mounted on the adjusting and connecting means web member inner face, and the adjusting and connecting means Web member forming with the support member an enclosure for the bus bar; the adjusting and connecting means being operative to move the tongue bus bar laterally toward and away from the support member, a screen deck extending beneath and abutting the lower face V 8 of the bus bar and being engaged over the bus bar tongue end, and means insulating the tongue bus bar from the support member.

sulation material; whereby the screen deck is prevented from grounding on the support member extending means.

5. Bus bar and support construction as defined in claim 2 in which the support member includes means extending beneath the lower face of the bus bar and screen deck; in which insulation means is positioned between the support member extending means and the screen deck for insulating the screen deck from the support member extending means; whereby the support member and adjusting and connecting means form substantially a complete enclosure for the bus bar, the screen deck is connected with the bus bar within the enclosure, and the screen deck is prevented from grounding on the support member extending means.

6. Composite skirt board construction for an electrically heated screen unit and the like, constituted by a longitudinally extending web with an upper border portion and a lower border portion and a face which in use is an outside face, the web upper border portion terminating in a free edge and the web being adapted for insulated mounting on a frame side member, a longitudinally extending tongue bus bar extending along the outside face of the lower border portion of the web, the tongue bus bar having a plurality of faces angular with respect to eachother and a plurality of lugs protruding beyondone of the faces, each lug having a hole formed therein, the web having holes formed therein, each web hole registering with one of the lug holes, a shanked connector for each set of registering holes connecting each of the lugs with the web thereby connecting the tongue bus bar with the web, and each shanked connector including a shank extending through the registering holes.

7. Bus bar and support construction including a tongue bus bar, a support member, laterally operating adjusting and connecting means operative between the tongue bus bar and the support member, the adjusting and connect ing means being operative to laterally move the tongue bus bar toward and away from the support member, means insulating the tongue bus bar from the support member, the tongue bus bar including a longitudinally extending portion having polygonal cross-section forming longitudinally extending V faces, the longitudinally extending V faces making an acute angle with each other and a junction with each other at an apex which is the outside edge of the bus bar, and the adjusting and connecting means including lugs protruding from the longitudinally extending portion of the tongue bus bar.

8. Bus bar and support construction as set forth in claim 7 in which the longitudinally extending portion of the tongue bus bar is solid.

9. Bus bar and support construction including a longitudinally extending tongue bus bar, a longitudinally ex.- tending frame support member; adjusting and connecting means operative between the tongue bus bar and the support member including a web member having an inner face opposite the support member and an outerface, lug means on the bus bar, and fastening means mounting. the lug mean on the adjusting and connecting means web member with the bus bar on the web member inner face; the adjusting and connecting means being operative to move the tongue bus bar laterally toward and away from the support member, a screen deck extending beneath the bus bar and having a longitudinally extending groove opening toward the adjusting and connecting means web member inner face, the screen deck being engaged over the bus bar with the bus bar in the screen deck groove, and means insulating the tongue bus bar from the support member.

10. In combination, a conducting screen deck having a first side and a second side, means supporting the first side of the screen deck; the second side of the screen deck having a longitudinally extending generally V-shaped groove opening toward the first side of the screen deck; a longitudinally extending support member adjacent the second side of the screen deck; a longitudinally extending tongue bus bar having a polygonal cross-section forming longitudinally extending V faces, said V faces making an acute angle with each other and a junction with each other at an apex extending toward said second side support member, and said apex being positioned engaged in said screen deck V-shaped groove; adjusting and connecting means operative between the tongue bus bar and the support member, the adjusting and connecting means being operative to move the tongue bus bar laterally toward and away from the support member; and means insulating the tongue bus bar from the support member.

11. The combination as defined in claim 10 in which the tongue bus bar has a solid polygonal cross-section.

12. Bus bar and support construction including a longitudinally extending tongue bus bar having a lower face and a tongue end portion, a longitudinally extending frame support member; adjusting and connecting means operative between the tongue bus bar and the support member including a web member having an inner face opposite the support member and an outer face, said web member having an upper border portion and a lower border portion, the bus bar being mounted on the web member inner face at said lower border portion and spaced from said support member, said web member upper border portion abutting said support member for pivotal movement with respect to said support member so that the web member forms with the support member an enclosure for the bus bar; the adjusting and connecting means being operative to move the tongue bus bar laterally toward and away from the support member by pivoting the web member upper border portion with respect to the support member, a screen deck extending beneath and abutting the lower face of the bus bar and being engaged over the tongue bus bar end, and means insulating the tongue bus bar from the support member.

References Cited in the file of this patent UNITED STATES PATENTS 1,397,342 Sturtevant Nov. 15, 1921 1,642,652 Gobiet Sept. 13, 1927 1,724,887 Schramm Aug. 13, 1929 2,053,561 Jennison Sept. 8, 1936 2,077,678 Delamater Apr. 20, 1937 2,122,298 Scott June 28, 1938 2,190,993 Muir Feb. 20, 1940 2,225,909 Gruender Dec. 24, 1940 FOREIGN PATENTS 225,310 Switzerland Apr. 16, 1943 

